The Sox and Forkhead (Fox) gene families are comprised of transcription factors that play important roles in a variety of developmental processes, including germ layer specification, gastrulation, cell fate determination, and morphogenesis. Both the Sox and Fox gene families are divided into subgroups based on the amino acid sequence of their respective DNA-binding domains, the high-mobility group (HMG) box (Sox genes) or Forkhead domain (Fox genes). Utilizing the draft genome sequence of the cnidarian Nematostella vectensis, we examined the genomic complement of Sox and Fox genes in this organism to gain insight into the nature of these gene families in a basal metazoan. We identified 14 Sox genes and 15 Fox genes in Nematostella and conducted a Bayesian phylogenetic analysis comparing HMG box and Forkhead domain sequences from Nematostella with diverse taxa. We found that the majority of bilaterian Sox groups have clear Nematostella orthologs, while only a minority of Fox groups are represented, suggesting that the evolutionary pressures driving the diversification of these gene families may be distinct from one another. In addition, we examined the expression of a subset of these genes during development in Nematostella and found that some of these genes are expressed in patterns consistent with roles in germ layer specification and the regulation of cellular behaviors important for gastrulation. The diversity of expression patterns among members of these gene families in Nematostella reinforces the notion that despite their relatively simple morphology, cnidarians possess much of the molecular complexity observed in bilaterian taxa.

The actin nucleation factors Spire and Cappuccino regulate the onset of ooplasmic streaming in Drosophila 1-5 . Although this streaming event is microtubule-based, actin assembly is required for its timing. It is not understood how the interaction of microtubules and microfilaments is mediated in this context. Here we demonstrate that Cappuccino and Spire have microtubule and microfilament crosslinking activity. The spire locus encodes several distinct protein isoforms (SpireA, SpireC, and SpireD). SpireD was recently shown to nucleate actin, but the activity of the other isoforms has not been addressed. We find that SpireD does not have crosslinking activity, while SpireC is a potent crosslinker. We show that SpireD binds to Cappuccino and inhibits F-actin/microtubule crosslinking, and activated Rho1 abolishes this inhibition, establishing a mechanistic basis for the regulation of Capu and Spire activity. We propose that Rho1, cappuccino and spire are elements of a conserved developmental cassette that is capable of directly mediating crosstalk between microtubules and microfilaments.Cytoskeletal elements must be coordinately regulated for cells to carry out complex functions, such as the cytoplasmic movements required to disperse or localize intracellular components 5 . The formin homology (FH) protein Cappuccino (Capu) and the WASP homology 2 (WH2) domain-containing protein Spire are both required for the proper timing of one such cytoplasmic movement, ooplasmic streaming in Drosophila 1,3 . In wildtype oocytes, vigorous ooplasmic streaming is associated with rapid growth during stages 10b-13, and is never observed prior to this stage. Mutations in capu and spire result in premature ooplasmic streaming, beginning at stage 7/8 and continuing through stage 13. This premature streaming interferes with transport mechanisms required for the localization of early polarity markers, resulting in disruption of dorsal-ventral and anterior-posterior body axes 1,2 . Both the wildtype streaming event and the premature streaming in capu and spire mutants are microtubule-based 1 . Streaming never takes place in oocytes lacking kinesin, and colcemid injection blocks premature streaming in these mutants 5,6 . Recent work suggests that streaming is restrained by the competing effects of dynein and kinesin, and can be initiated by blocking dynein function 7 . Thus, it is somewhat paradoxical that Spire and Capu nucleate actin, but are not known to affect microtubule architecture or dynamics. Interestingly, the premature streaming seen in capu and spire mutant oocytes can be recapitulated by injection of the actindepolymerizing drug cytochalasin D into wildtype oocytes, suggesting that actin assembly may restrict microtubule rearrangements required for ooplasmic streaming 8 . Presumably, microtubule and microfilament dynamics are coordinated in oogenesis by a group of proteins that includes Spire and Capu, as well as one or more upstream signals. However, the signaling events that combine to encode a "switch" from the n...

Gastrulation is a central event in metazoan development, involving many cellular behaviors including invagination, delamination, and ingression. Understanding the cell biology underlying gastrulation in many different taxa will help clarify the evolution of gastrulation mechanisms. Gastrulation in the anthozoan cnidarian Nematostella vectensis has been described as a combination of invagination and unipolar ingression through epithelial to mesenchymal transitions (EMT), possibly controlled by snail genes, important regulators of EMT in other organisms. Our examination, however, fails to reveal evidence of ingressing cells. Rather, we observe that endodermal cells constrict their apices, adopting bottle-like morphologies especially pronounced adjacent to the blastopore lip. They retain apical projections extending to the archenteron throughout gastrulation. Basally, they form actin-rich protrusions, including interdigitating filopodia that may be important in pulling the ectodermal and endodermal cells together. Endodermal cells retain cell-cell junctions while invaginating, and are organized throughout development. Never is the blastocoel filled by a mass of mesenchyme. Additionally, injection of splice-blocking morpholinos to Nematostella snail genes does not result in a phenotype despite dramatically reducing wild-type transcript, and overexpression of Snail-GFP in different clonal domains has no effect on cell behavior. These data indicate that EMT is not a major factor during gastrulation in Nematostella.